The nude mouse CBA congenic backcross is now available for further investigations on susceptibility of this to three forms of human viral hepatitis. This year a pilot study was initiated exposing the CBA nude to filtrated stool containing the antigen of human hepatitis A. Rapid death in all inoculated animals ensued, most likely due to an endotoxin in the fecal filtrate. Additional pilot studies with hepatitis A are now being planned. Hepatitis B and hepatitis non-A, non-B will also be inoculated into these mice during the summer of 1979.